A hammer drill often has three modes of operation. Such a hammer drill typically comprises a spindle mounted for rotation within a housing which can be selectively driven by a rotary drive arrangement within the housing. The rotary drive arrangement is driven by a motor also located within the housing. The spindle rotatingly drives a tool holder of the hammer drill which in turn rotatingly drives a cutting tool, such as a drill bit, releasably secured within it. Within the spindle is generally mounted a piston which can be reciprocatingly driven by a hammer drive mechanism which translates the rotary drive of the motor to a reciprocating drive of the piston. A ram, also slideably mounted within the spindle, forward of the piston, is reciprocatingly driven by the piston due to successive over and under pressures in an air cushion formed within the spindle between the piston and the ram. The ram repeatedly impacts a beat piece slideably located within the spindle forward of the ram, which in turn transfers the forward impacts from the ram to the cutting tool releasably secured, for limited reciprocation, within the tool holder at the front of the hammer drill. A mode change mechanism can selectively engage and disengage the rotary drive to the spindle and/or the reciprocating drive to the piston. The three modes of operation of such a hammer drill are; hammer only mode, where there is only the reciprocating drive to the piston; drill only mode, where there is only the rotary drive to the spindle, and; hammer and drill mode, where there is both the rotary drive to the spindle the reciprocating drive to the piston.
EP1157788 discloses such a hammer.
While such hammer drills often comprise three modes of operation, it is also fairly common for hammer drills to only have either one or two modes of operation. For example, there are many types of hammer drills which only have drill only mode and which are more commonly referred to as a drill. One type of such a hammer drill is pavement breaker.
A pavement breaker is a hammer drill having only a single mode of operation, namely that of hammer only mode (sometimes referred to as chisel mode). Pavement breakers tend to be relatively large hammer drills, the weight of which being capable of being used to assist in the operation of the pavement breaker. Though theoretically it is possible to fully support a pavement breaker in the hands of the operator, typically their weight prohibits this or at least limits the amount that this can be done. As such, when manually manoeuvred, pavement breakers are typically utilised in a downward projecting manner so that the tool held in the tool holder is in contact with the ground, the weight of the pavement breaker being transferred to the ground through the cutting tool.
EP1475190 discloses a pavement breaker.
During the operation of a pavement breaker, the ram within it repeatedly strikes, via a beat piece, a cutting tool, such as a chisel, held within a tool holder located at the lower end of the body of the pavement breaker.
FIGS. 1 to 6 show a typical prior art design of tool and tool holder for a pavement breaker.
Referring to FIG. 1, the design of a cutting tool, such as a chisel, which can be used with these types of pavement breaker will now be described.
The tool comprises a working end (not shown) which engages with a work piece, such as a concrete floor, formed onto one end of a shank 400. The shank 400 has a hexagonal cross section in shape and a longitudinal axis 408. The other connection end 402, opposite to the working end, comprises a connection mechanism.
The first type of connection mechanism is in the form of rib 404 formed around the circumference of the shank 400 and which is located at a predetermine distance from the remote end of the connection end 402 of the shank. The second type of connection mechanism is in the form of recess 406 formed on one side of the shank 400 along part of the length of the shank 400 at a predetermined distance from the remote end of the connection end 402 of the shank. The third type, which is shown in FIG. 1, comprises both the rib 404 and the recess 406.
A tool with the first type of connection mechanism is intended to be used with a first type of tool holder which can engage with and hold the rib 404. A tool with the second type of connection mechanism is intended to be used with a second type of tool holder which can engage with the recess 406 to hold the tool. A tool with the third type of connection mechanism is intended to be used with either the first type of tool holder capable of holding a tool with the first type of connection mechanism, the second type of tool holder capable of holding a tool with a second type of connection mechanism, or a tool holder capable of holding a tool with the third type of connection mechanism.
However, there are designs of tool holder which are capable of holding tools with any of the three types of connection mechanism. Such a tool holder will now be described.
Referring to FIG. 1, the tool holder 500 comprises a tool holder housing 502 which is formed from a single metal cast which is attached to a middle housing 504 using a series of standard bolts 506. A plurality of holes 508 are formed through a flange 510 formed around the upper end of the tool holder housing 502. Corresponding holes 512 are formed through the base 514 of the middle housing 504. The bolts 506 pass through the holes 508 in the flange 510 of the tool holder housing 502 and then through the holes 512 through the base 514 of the middle housing 504. Standard nuts 518 are screwed onto the ends of the bolts 506 adjacent the base 514 of middle housing 516 to secure the tool holder housing 502 to the middle housing 504.
Integrally formed in the tool holder housing 502 is a tubular recess 520 of hexagonal cross section which is intended to receive the connection end 402 of the shank 400. The hexagonal cross section of the recess 520 and corresponding hexagonal cross section of the shank 400, and their respective sizes, prevent rotation of the tool within the recess 520.
A tubular passageway 522 is formed across the width of the tool holder housing 502. The cross sectional shape of the tubular passageway 522 is oval. The tubular passageway 522 intersects the top part of the tubular recess 520 at its centre. A metal rod 524, of circular cross section, passes through the full length of the tubular passageway 522, the ends 526 extending outwardly on either side of the tool holder housing 502. The centre 560 of the metal rod 524 comprises a circular groove 528 formed widthways, the maximum depth of which at its centre being half that of the width of the metal rod 524. The centre of the metal rod 524, which includes the groove 528, is located in and traverses across the top part of the tubular recess 520.
The metal rod 524 can freely rotate about its longitudinal axis 530 within the tubular passageway 522, the longitudinal axis 530 of the metal bar 524 being parallel with that of the tubular passageway 522. The oval shape of the passageway enables the bar 524 to slide in a direction (indicated by Arrow M) parallel to that of the longitudinal axis 408 of the tool when the tool is located within the tool holder 500.
Rigidly mounted onto the two ends 526 of the metal rod 524 is a U shaped clamp 532. The U shaped clamp 532 comprises two ends 534 which are in the form of rings. The two bar holes 536 of the rings 534 are co-axial and face each other. Attached to each end ring 534 is a curved arm 538. The ends of both the curved arms 538 connect to a semi-circular hook 540 as best seen in FIG. 100. The inner diameter of the hook 540 is greater than that of the shank 400 but less than that of the rib 404 of the tool. The end rings 534, the curved arms 538 and the hook 540 are manufactured from steel in a one piece construction.
Holes 542 are formed through the ends 526 of the metal bar 524, the axes of the holes 542 being parallel to each other and perpendicular to the longitudinal axis 530 of the metal bar 524. Holes 544 are formed through the end rings 534 of the U shaped clamp 532, the axes of the holes 544 being parallel to each other and perpendicular to the axis of the bar holes 536 of the end rings 534. The ends of the metal bar 524 locate within the bar holes 536 of the end rings 534 and orientated so that holes 542 of the metal bar 524 and the holes 544 of the end rings 534 are aligned (see FIG. 4). A pin (not shown) passes through each set of aligned holes 542, 544 to rigidly attach the end rings 534 to the ends 526 of the metal bar 524.
The metal rod 524 is held within tubular passageway 522 by two compressible rubber rings 546 which locate within cavities 548 formed in the side of the tool holder housing 502 (see FIG. 1). The rubber rings 546 bias the metal rod 524 to a central location within the tubular passageway 522. However, by compressing the rubber rings 546, the metal rod 524 can be moved within the oval tubular passageway 522 in a direction (Arrow M) parallel to the longitudinal axis 408 of the tool.
The U shaped clamp 532 pivots, in unison with the metal rod 524, about the longitudinal axis 530 of the metal rod 524. Pivotal movement of the U shaped clamp 532 locks the tool 400 within the tool holder or releases it.
The U shaped clamp 532 itself is used to hold a tool with the first type of connection mechanism by engaging with the rib 404 of the tool. The U shaped clamp 532 is pivoted to a position where the tubular recess 520 is exposed. (It should be noted that U shaped clamp 532 will be in a position where the circular groove 528 of the metal bar 524 faces towards the tubular recess 520 so that the metal bar 524 does not interfere with the insertion of the connection end 402 of the tool). The connection end 402 of the tool is inserted into the tubular recess 520 until the rib 404 engages with the nose 550 of the tool holder housing 502. The U shaped clamp 532 is then pivoted until the hook 540 of the U shaped clamp 532 surrounds the shank 400 of the tool below the rib 404. In this position, the rib 404 is prevented from travelling past the hook 540 of the U shaped clamp 532. As the connection end 402 of the tool slides out of the tubular recess 520, the rib 404 engages with the hook 540 of the U shaped clamp 532 and is then prevented from travelling further. As such, the connection end 402 of tool is held within the tubular recess 520 whilst being able to slide axially over a limited range of travel, the range of movement being the distance the rib 404 can slide between the nose 550 and the hook 540 (as best seen in FIG. 3). To release the tool, the U shaped clamp is pivoted so that the hook is removed from the path way of the rib 404, to allow the connection end 402 to fully slide out of the tubular recess 520.
A first locking mechanism is provided for U shaped clamp 532 so that, when the hook surrounds the shank 400 to lock the tool within the tool holder, the U shaped clam 532, including the hook 540, is locked in that position to prevent the tool inadvertently being released from the tool holder. Formed on the periphery of the two rings 534 of the U shaped clamp 532 are first flat locking surfaces 552. Formed on the tool holder housing 502 are corresponding flat holding surfaces 554. When the hook 540 surrounds the shank 400 to hold the tool in the tool holder, the flat locking faces 552 and the flat holding surfaces 554 are aligned with each other and are biased together by the rubber rings 546 (which biases the metal bar 524 in the direction of Arrow M to a central position within the tubular passageway 522) so that they abut against each other (see FIG. 5—solid lines). As the surfaces 552, 554 are flat and are biased together, the rings 534 are prevented from rotating. In order to rotate the rings 534, and hence pivot the U shaped clamp, the U shaped clam 532 has to move axially (direction of Arrow M) to allow the flat locking faces 552 to pivot relative to the flat holding surfaces 554 (see dashed lines in FIG. 5). The axial movement (Arrow M) of the U shaped clamp 532 is achieved by the compression of the rubber rings 546 within the cavities 548 which allow the metal bar 524 to slide within the oval tubular passageway 522. Pivotal movement of the U shaped clamp 532 causes the rubber rings 546 to compress, allowing the first flat locking surfaces 552 to ride over the flat holding surfaces 554. The biasing force of the rings 546 hold the locking surfaces 552 against the holding surfaces 554 and hence lock the U shaped clamp 532 in the locking position.
The metal rod 524 itself is used hold a tool with the second type of connection mechanism by engaging with the recess 406 of the tool. The metal rod 524 is pivoted to a position where the U shaped clamp 532 is located away from the location of the tool, leaving the recess 520 exposed. The precise position of the U shaped clamp 532 is such that the circular groove 528 of the metal bar 524 faces into the tubular recess 520. As such, there are no restrictions within the tubular recess 520 to prevent the connection end 402 of the tool 400 fully entering the tubular recess 520.
The connection end 402 of the tool is fully inserted into the tubular recess 520. It has to be ensured that the recess 406 of the tool 400 faces upwards towards the metal bar 524. (It should be noted that the tool can not be rotated within the recess 520 due to the cross sectional shapes of the shank 402 and the recess 520.)
When the connection end 402 of the tool 400 is fully inserted into the tubular recess 520, that the groove 528 of the metal bar 524 faces into recess 406 of the tool.
The U shaped clamp 532 is then pivoted, causing the metal bar 524 to pivot, until the groove 528 of the metal bar 524 faces away from the recess 406 of the tool. At this point, the central part 560 of the metal bar 524 faces towards and locates within the tubular recess 520 of the tool holder and thus faces towards and locates within the recess 406 of the tool 400. This is best seen in FIG. 2.
In this position, the upper 412 and lower 414 edges of recess 406 are prevented from travelling past the central part 560 of the metal bar 524. As the connection end 402 of the tool slides out of the tubular recess 520, the upper edge 412 engages with the central part 560 of the metal bar 524 and is then prevented from travelling further. As such, the connection end 402 of tool is held within the tubular recess 520 whilst being able to slide axially of a limited range of travel, the range of movement being the distance the central part 560 can slide between the upper 412 and lower 414 edges of the recess 406 (as best seen in FIG. 2).
To release the tool, the U shaped clamp 532 is pivoted in order to pivot the metal bar 524 in order to remove the central part 560 of the metal bar 524 from the recess 406 of the tool 400, which allows the connection end 402 of the tool to fully slide out of the tubular recess 520.
A second locking mechanism is provided for U shaped clamp 532 so that, when the central part 560 of the metal bar 524 is located within the recess 406 of the tool 400 to lock the tool 400 within the tool holder, the U shaped clam 532, including the metal bar 524, is locked in that position to prevent the tool inadvertently being released from the tool holder. Formed on the periphery of the two rings 534 of the U shaped clamp 532 are second flat locking surfaces 562. As described previously, formed on the tool holder housing 502 are flat holding surfaces 554. When the central part 560 of the metal bar 524 is located within the recess 406 of the tool 400 to hold the tool in the tool holder, the second flat locking faces 562 and the flat holding surfaces 554 are aligned with each other and are biased towards each other by the rubber rings 546 so that they abut against each other (see FIG. 6—solid lines). As the surfaces are flat, the rings 534 are prevented from rotating. In order to rotate the ring and hence pivot the U shaped clamp 532 and the metal bar 524, the U shaped clam 532 has to move axially (direction of Arrow M) to allow the second flat locking faces 562 to pivot relative to the flat holding surfaces 554 (see dashed lines in FIG. 6). The axial movement of the U shaped clamp 532 is achieved by the compression of the rubber rings 546 within the cavities 548 which allow the metal bar 524 to slide within the oval tubular passageway 522. Pivotal movement of the U shaped clamp 532 causes the rubber rings 546 to compress, allowing the second flat locking surfaces 562 to ride over the flat holding surfaces 554. The biasing force of the rings 546 hold the second locking surfaces 562 against the holding surfaces 554 and hence lock the U shaped clamp 532, and hence the metal bar 524, in the locking position.
Such a tool holder can hold all tools with any of the three types of connection mechanisms.
During the operation of a pavement breaker having such tool holder, the beat piece 564 repeated strikes the connection end 402 of the tool 400. The diameter of the head 566 of the beat piece 564 is greater than that of the tubular recess 520 required to receive the connection end 402 of the tool 400. As such, the top end 568 of the tubular recess 520 has an increased diameter to enable the head 566 of the beat piece 564 to travel along the length of the top end 568 of the tubular recess 520.
Forward, downward movement of the beat piece 564 along an axis 570 (parallel to the longitudinal axis of the tool 400 when held within the tool holder) is limited by a front shoulder 572 of the head 566 of the beat piece 564 engaging with a lower stop 574 formed between the top end 568 section of the tubular recess 520 and the remainder of the tubular recess 520.
Rearward, upward movement of the beat piece 564 along the axis 570 is limited by a rear shoulder 576 of the head 566 of the beat piece 564 engaging with an upper stop 578 formed on a side of a metal ring 580 rigidly attached to the top end of the tool holder housing 502.
The tool holder and beat piece 564 support structure, which includes the top end section 568 of the tubular recess 520 and the metal ring 580, are designed so that when it used to hold a tool having the first type of connection mechanism, the rib 404 is always able to engage with the nose 550 of the tool holder housing 502. When the connection end 402 of the tool 400 is inserted into the tubular recess 520, it engages with the head 566 of the beat piece 564, which is biased downwardly due to gravity, and pushes it upwardly. As the connection end 402 slides into the tubular recess 520, it pushes the beat piece upwardly against the biasing force of gravity. The design of the tool holder and beat piece 564 support structure is arranged so that the rib 404 always engages with the nose 550 of the tool holder housing 502 prior to the rear shoulder 576 of the head 566 of the beat piece 564 engaging with the upper stop 578 formed on a side of the metal ring 580 rigidly attached to the top end of the tool holder housing 502.
Pavement breakers generate a great deal of vibration during its operation. In order to make a pavement breaker as user friendly as possible, it is desirable to minimise the amount of vibration experienced by the operator as small as possible. One method of achieving this is to use a dampening mechanism to counteract the vibration generated by the operation of the pavement breaker. EP1252976 discloses a hammer drill having such a dampening mechanism.
EP1252976 shows a hammer drill having a cylinder, a piston reciprocatingly driven within the cylinder by a motor, a ram slideably mounted within the cylinder which is reciprocatingly driven by the piston via an air spring, and a beat piece which is repetitively struck by the ram and which, in turn, strikes an end of a cutting tool, such as a chisel, held within a tool holder. An oscillating counter mass is used to reduce vibration within the hammer drill. The counter mass surrounds and is slideably mounted on the cylinder and is held between two springs which bias the counter mass to a predetermined position on the cylinder. The mass of the counter mass and the strength of the springs are such that, when the hammer drill is operated, the counter mass vibrates out of phase with the piston and ram so that it counteracts the vibration generated by the operation of the hammer drill.
During the normal operation of a pavement breaker, the beat piece strikes the end of the tool, causing the head 566 of the beat piece 564 to become worn. The amount of wear on the beat piece generally is determined by dismantling the pavement breaker to visually inspect the beat piece. Excessive wear to the beat piece can result in damage in the internal workings of the pavement breaker as well as a deterioration in performance.